The present invention relates generally to alarm apparatus for use in cable television (CATV) systems and particularly concerns an improved alarm control circuit for controlling an alarm apparatus operated in response to signals provided by a CATV decoder which receives alarm messages from a head-end facility over a CATV network.
Addressable CATV systems comprise head-end facilities which transmit television programming and data signals through a CATV network for receipt by special decoders installed for operating the television receivers of system subscribers. Typically, one or more tiers of programming signals are transmitted in encoded or scrambled form and must be properly decoded or unscrambled by a subscriber's decoder before being applied to the television receiver for reproduction. Numerous techniques for encoding the video portion of a transmitted television signal are well known in the art and include video signal polarity inversion and synchronization signal suppression. Each subscriber's decoder is authorized for decoding selected tiers or categories of programming signals according to the payment of prescribed fees, the decode authorization status of the decoder being automatically effected by data messages transmitted from the head-end facility to the decoder through the CATV network. These data messages may be encoded in the transmitted television signal itself; for example, the data may be inserted as logic bits in the vertical intervals of the broadcast television signal, or they may be transmitted on an out-of-band carrier. In either event, it will be appreciated that the data messages provide a convenient facility for transmitting information such as decoder authorization status from the head-end facility to the system subscribers via the CATV network.
It has recently been proposed to utilize this communications facility for providing a wide variety of information from the CATV head-end to the system subscribers. It has in particular been proposed to transmit emergency and other alert messages which can be processed by a subscriber's decoder for activating an alarm or other indicator to alert the subscriber of some condition. The alert condition could be of general interest to the entire subscriber population, e.g. a severe weather warning, in which case all of the subscribers would be alerted. Alternatively, the alert could be of a more narrowly defined nature such as an alert directed to the volunter firemen in the community. In any case, there is currently a need in an addressable CATV alert system of this general type for an improved subscriber operable apparatus for controlling alarm generation and, specifically, there is a need for an inexpensive subscriber control circuit which is convenient to use and which will provide for full subscriber control over the generation and override or cancelling of an alarm indication.
It is therefore a general object of the present invention to provide an improved subscriber operable control circuit for an addressable CATV emergency/alert system.
It is a more specific object of the invention to provide an improved subscriber operable alarm control circuit for an addressable CATV emergency/alert system in which one single-pole switch is displaceable between two switching positions for enabling, disabling, and clearing an alarm generating circuit.